Abstract:When a fluid in a tube is occluded, one finds a static configuration in which the
occluding free surface of the fluid is an equilibrium capillary surface spanning the tube.
We extend known criteria for existence and non-existence of such a surface, leading to an
explicit mathematically rigorous occlusion criterion for cylindrical tubes in a transverse
body force field, depending on the force magnitude and contact angle. For any contact
angle γ ≠ π/2, we provide further an explicit design of a tube section, which will not
occlude in a downward gravity field, regardless of the field strength. In addition we derive
a precise analytic occlusion criterion for a circular vessel spinning about its axis.